Hazardous fluids are routinely conveyed within enclosed pipes or conduits. Recognizing that such pipes and conduits can leak due to manufacturing defects, excessive pressure, corrosion, and joint defects, for example, which may be due to thermal stresses, double-containment piping systems have been developed in which an inner or primary pipe is located within an outer or containment pipe forming an annulus between the inner and outer pipes. The annulus is typically dry, except in the event of a leak of fluid carried by the inner pipe. The inner pipe is typically supported by resting directly on the lower, inside wall of the outer pipe. Alternatively, support apparatus are provided in which the inner pipe is supported in spaced relation to the inside wall of the outer pipe. Exemplary supports are illustrated in the following U.S. Pat. Nos. 5,141,184; 5,018,260; 4,751,945; 3,863,679; and 3,417,785.
Although such prior supports may be used to support the inner pipe within the outer pipe, and provide ready access to the inner pipe at spaced locations along the outer pipe, such supports are typically joined to the inner pipe and/or the outer pipe by welding or bonding means to secure the support in place. The welding or bonding process can require significant construction and assembly time, which results in added project costs, and further prolongs the installation time of the double-containment piping system. The welding or bonding process also typically requires that the support be made of the same material as either the inner or the outer pipe so that it can be adequately welded or bonded to the respective pipe. Accordingly, any flexibility in selecting the material for the support is frequently limited by the materials of the inner and outer pipes.
Prior supports also frequently directly support an inadequate portion of the inner pipe in comparison to that which is typically required for single-wall above-ground pipes. For example, there are one-piece collar-type supports which by design fit less than perfectly around the external circumference of the inner pipe, in order to slip the support into position over the inner pipe. This type of collar support is then secured in place typically by welding or otherwise bonding the support to the inner pipe. Thus, although such a support may surround the inner pipe, it typically does not maintain sufficient support of the entire circumference of the inner pipe because its inner diameter is inherently greater than the outer diameter of the inner pipe. This is a particular disadvantage with fiberglass pipes, which typically require uniform support along the entire circumference of the inner pipe.